PIC Notes - Feb 25

PIC Notes, Feb 25

I have ordered four more programmers which will bring us to six. This should alleviate some congestion and frustration. However, it will still be necessary for those groups using a PC with a programmer to yield to other students.
Be sure to download lcd_new.asm to your a: floppy. This contains the new DEBUG function. Your #include statement at the bottom of your routines will now reference a:\lcd_new.asm.
As noted in class, the displays the value of the W register and the state of the Z and C flags on line one. It displays the content of locations 10-17H on lines 3 and 4. It displays this for one second and then returns to the calling program. This should prove helpful in debugging your routines.
To date, we have been assigning variables beginning at 0CH. You may want to begin assigning variables which you may want to examine at location 10H. That is;
```
	CONSTANT BASE = $10
	...

	ORG 000H

	TICK_HI	EQU BASE+0
	TICK_LO EQU BASE+1
```
If you are having trouble with your routine, insert calls to DEBUG to display the various values;
```
	CALL DEBUG
```
Please download a copy of PULSIN.ASM. Be sure you understand everything in this routine.
Assignment. 1. Build the 555 circuit and observe the high and low times. Modify the PULSIN routine as necessary to measure the number of 5 usec ticks. Display the number of ticks in hex. As this is a word (two bytes) it will require displaying the hgih byte and then the low byte using the LCD_VAL routine.
As you heat the thermistor with your hand, you should see a definite change in the number of 5 usec ticks. You should be able to expalin the value you are getting. That is, at room temperature, the nominal R_therm is 10K. The T_555_LO is of some value and the number of 5 usec clock ticks should agree with this.
2. A side show. Displaying a word (two bytes) in hex is not always desireable. Develop a subroutine to convert a two byte hex number such that it can be displayed in decimal. I will discuss this more on Monday.
3. The balance should be done using Quattro.
Calculate the theoretical number of TICKs at 50 and 90 degrees F.
Develop a spreadsheet with 256 equally spaced points between TICKS_90 and TICK_50, and for each of these points calaculate T_555_LO, R_therm, T_Kelvin, T_cel and T_F.
The important thing is T_F. Thus, we have a table of 256 values of TICKs and the resulting temperature in degrees F.
In the next portion, we will use this to develop a lookup table that takes the number of TICKS and maps it to an index and we fetch the resulting temperature.
Thus, in your interview, I will be looking for a demo that is continually displaying the number of TICKs as a result of measuring the 555. This uses the PIC. And, a speadsheet which doesn't use the PIC.
Keep up the good efforts!